1. Field of the Invention
The present invention relates to techniques for effecting repairs in aircraft structures, and more particularly to techniques for effecting field fabricated patches in convolved structural members.
2. Description of the Prior Art
In my prior U.S. patent application Ser. No. 553,575, filed on Nov. 21, 1983 and issued as U.S. Pat. No. 4,517,038 on May 14, 1985 I have described a technique for effecting repairs in structural members which can be conveniently carried out in the field. As stated therein military aircraft, and particularly military aircraft dedicated to close ground support in the course of conflict, often suffer ballistic damage as result of ground fire. Characteristically such ballistic damage entails tears and cracks which thereafter form points of stress concentration from which further fracture propagation occurs. For this reason ballistic damage is preferrably repaired immediately, particularly if such damage occurs in a stressed surface or a surface carrying aerodynamic loads.
Aerodynamic surfaces, in many instances, involve curved surface shapes, where the curvature of the panel is often used beneficially to carry load. Thus, quite often an airplane structure includes sections of semi-monocoque structure which are contiguous to sections of full monocoque form. The semi-monocoque configurations, as is well known in the art, resolve most of the stress transfer by way of stringers and spars with the skin therebetween being loaded mainly in shear. Monocoque structures, however, impose loading on the skin surface not just in shear but also entailing components of compressive tensile and bending load. Accordingly, any damage to a monocoque structural element, such as damage from a ballistic projectile, will entail concentrations of stress in all of the foregoing modes. For this reason, repair of such damage is a matter of great structural significance and techniques for conveniently effecting such repair have been sought in the past. Heretofore such techniques typically entailed the replacement of the whole panel segment, a replacement which, in the course thereof utilizes the replacement of the original fasteners and thus involves complex procedures not convenient in the field.
Accordingly, techniques for convenient field panel repair have been sought in the past and it is one such technique that is disclosed herein.